The present invention relates to a method of producing chlorinated EVA, in more detail, to a method of obtaining solvent-soluble chlorinated EVA useful as a resin for printing ink, wherein the chlorinating reaction is conducted at an optimum temperature depending on the content of vinyl acetate while suspending EVA powder containing 5 to 35 wt. % of vinyl acetate into aqueous medium.
As can be seen in Japanese Patent Publication No. sho 47-46203, the solvent-soluble chlorinated EVA has been obtained so far by a method of conducting the chlorinating reaction after dissolved EVA into a chlorine-resistant organic solvents such as carbon tetrachloride etc. and is widely used as a resin for printing ink based on the features such as transparency and gloss.
In recent, however, the influences of organic solvents on the human body and the global environment have become anxious worldwide and the use of organic solvents has to be severely restricted also from a legal point of view. In particular, with respect to a part of organic halides, a proposal appealing for the overall abolition of use was presented to the international conference and it is the situation that the related industries are driven by the investigations to alternatives or replaceable techniques.
Thus, the inventors investigated a production method of chlorinated EVA not using organic solvents such as carbon tetrachloride etc. and found that most of the conventional methods for chlorinating polyolefin etc. in aqueous suspension related to the production methods for molding materials as can be seen in Japanese Unexamined Patent Publication No. sho 51-138791 etc., and it is common knowledge that the solubility in solvent is insufficient primarily due to the inhomogeneous chlorination and thus partially remaining crystallinity.
Further, with respect to the chlorinating method of EVA in aqueous suspension, it is dealt with very often similarly with the chlorinating methods of polyethylene (Japanese Unexamined Patent Publication No. sho 61-179205 and No. sho 53-146793), thus it is the present status that the melt-bonding and lumping occurring during the reaction cannot be prevented because of inadequate reaction conditions. Although such methods are known as the measures therefor that water-soluble polymers or organic or inorganic fine powders are added (Japanese Patent Publication No. sho 46-21729 and No. sho 46-21887), incorporation thereof would provide adverse effects on the performance of chlorinated EVA if remaining as they are, and yet the removal thereof is rather difficult.
Based on these facts, it can be said as an important theme for solving the social problem aforementioned to find out an optimum method of producing chlorinated EVA useful as a resin for printing ink by the aqueous suspension method not using halogenated organic solvents such as carbon tetrachloride etc.
As a result of extensive investigations for solving said theme, the inventors have found the following leading to the completion of the invention.